Alternative Layered-Structure SiCu Composite Anodes for High-Capacity Lithium-Ion Batteries

Si-based thin films have attracted increasing attention as the anode of lithium-ion microbatteries (LIMBs) because of their high capacity in the field of microelectronics. In this work, the SiCu composites film was directly co-electrodeposited on the Cu substrate in 0.002 mol/L Cu(TfO)2–1 mol/L SiCl4-[BMP]Tf2N ionic liquid at −1.9 to −2.1 V for 1 h. SiCu films have shown alternative layer structure consisting of Cu-rich and Si-rich layers caused by the much large molar ratio of Si4+/Cu2+ ions in the ionic liquid and the different reduction capacity of Si4+ and Cu2+. Both of the Cu-rich and Si-rich layers had a porous structure, which was generated by the volatile SiCl4 bubble formation and attachment on the SiCu film during the co-electrodeposition processes. The Si-rich layer was mainly comprising several Si lamellas attached with Si particles and a small amount of about 5–6 nm Cu particles. It is worth noting that the introduction of Cu contributes to generate flake-stacked structure and enhance the conductivity of Si-based films. SiCu composites manifest satisfactory cycle stability as the LIB anode material; for instance, the specific capacity of SiCu electrodeposited at −1.9 V remains at 1356 mAh/g after 750 cycles at a current density of 4 A/g with 90% capacity retention, as well as 1042.8 mAh/g after 600 cycles at a current density of 21 A/g with 87.7% capacity retention. These excellent performances are attributed to the porous and stacked flake Si-based structure. This finding provides a new idea for the direct design of a well-structured composite material by controlling electrolyte composition and potential.